Best value 21700 cell - LG M50L or LG M48?

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koo

100 µW
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Nov 13, 2013
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Planning on building two or three 48V batteries to get extended range on Bafang BBS02b, and I stumbled upon LG M48 and LG M50L as great options, costing around 1.60e for M48 and 2.1euro for M50L from nkon.

I know the M50L has been tested on the forum and performs well. The datasheet also lists 1000+ cycles that corresponds with the testing. I couldn't find a datasheet for M48, and if their labeling is consistent with how M50 is inferior to M50L in number of cycles and degradation, I'm hesitant to pull the trigger M48. M48F datasheet snippets I've seen look fine enough, but it's probably different model.

Additionally, my XTAR VC4SL is testing the dozen M50L I already bought from nkon at around 4600-4700 at IR of 50-80mOhm. Not great, not awful. Of course the measurements from the charger should be taken with a grain of salt since its a cheap charger.

What would you guys do, pay the extra 25% for M50L or "gamble" a bit with the M48? I'll probably buy 130-150 cells to build two 1KWh packs and do ride -10C temps as well, so also need to be mindful of how much current gets drawn since LG lists 0.5C discharge rate for 10C to -20C.
 
A BBS02 peaks at 25A but the rated 750W power is 15A @ 48V. That's 3A continuous on a 5P and 2.5A on a 6P. Newer Molicel 21700 datasheets don't appear to have a .5C rating for cold ambient operation. If you're going to ride your BBS02B at -10C, I guess you want to build a 6P and choose the cells with the highest capacity for cold weather, whichever one that is.

By the way, I have read that if you start off slowly at cold temperatures, that the internal cell temperatures will rise. Each cell is generating 5 watts of heat after all. While I rarely ride my ebikes below 5C, I want to be at least 10C for recharging, so I count on the batteries warming up.

Meanwhile, 2.1€ for an ML50 is pretty cheap. I didn't see these on the english nkon website. Are these clearance prices for old stock? Anyway, for 150 cells, the difference is 75€, not worth worrying about..

I would not trust the IR on your XTAR tester.
 
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docw009 said:
A BBS02 peaks at 25A but the rated 750W power is 15A @ 48V. That's 3A continuous on a 5P and 2.5A on a 6P. Newer Molicel 21700 datasheets don't appear to have a .5C rating for cold ambient operation. If you're going to ride your BBS02B at -10C, I guess you want to build a 6P and choose the cells with the highest capacity for cold weather, whichever one that is.

By the way, I have read that if you start off slowly at cold temperatures, that the internal cell temperatures will rise. Each cell is generating 5 watts of heat after all. While I rarely ride my ebikes below 5C, I want to be at least 10C for recharging, so I count on the batteries warming up.

Meanwhile, 2.1€ for an ML50 is pretty cheap. I didn't see these on the english nkon website. Are these clearance prices for old stock? Anyway, for 150 cells, the difference is 75€, not worth worrying about..

I would not trust the IR on your XTAR tester.
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Really useful feedback, thank you! I was planning on 13S5P build but now may have to consider 13S6P. Realistically I don't think I'll be drawing 750w continuously for extended times anyways but its nice to have that option. Easy to use lower assist levels when starting with a cold battery. And it makes more sense to have 0.5C rating at -20C while at 0C or -5C perhaps 0.7 or 1C is fine. At worst, it's a little faster degradation and I doubt I'll use 1000 cycles on the battery anyways... Here's the NKON listing, 2.05e when buying +130 cells.

Looks like I'll be pulling the trigger on the M50L cells, now just need determine how many I need!
 
docw009 said:
Each cell is generating 5 watts of heat after all.
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How is that so? If you have like 60 cells in the battery, would it generate 300W of heat? I think there's some heat coming from the cells, but order of magnitude less than that.

(Edit):
looks like it could be 5W if you discharge each cell with at least 10A current, which is well above what they're capable of - but still your estimate is closer to reality than what i initially thought. Just not possible to get that level of heating in below zero temperature, datasheet says you can get 2A only and about ~0.2W of heating.
 
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Yes, I am wrong. Each cell is generating 4V x 1 amp = 4 watts, but only a few percent of that is heat. That is more like 5 watts for the whole battery,
 
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